At Universal during our past visits, we've seen many characters on Hollywood blvd near the end of the day, around 4pm.
There is a nice character meet and greet in Woody Woodpecker kidzone with Scooby, feivel, Woody Woodpecker,etc

At IOA, DH and I got pictures with Cat in the Hat and Thing 1 and Thing 2 early at IOA, around 9:30, at the entrance to Seuss landing.